Which is the best affiliate program?

I think it depends on your niche.

I found this list somewhere so want to share it with you
http://www.jdoqocy.com
http://valueclick.com
http://www.linkshare.com
http://www.leadcreations.com
http://www.shareasale.com
http://directleads.com
http://www.focalex.com
http://www.fineclicks.com
http://www.allclicks.com
http://www.clickxchange.com
http://www.leadhound.com
http://publishers.clickbooth.com
http://www.clixgalore.com

Become an affiliate for products on the basis of your website theme and then simply promote these programs where you can earn money from referrals. You simply sign up for these paid online survey sites, fill out the questions, and earn a fixed sum of money every time you complete one. You can also add affiliate links on your blogs and Google Adsense to earn more money. Although many still earn a crust doing manual work, the real bucks to be had are quite often found in the virtual world. Despite the fact that pay scales and methods can vary greatly, you also have the potential to earn money and over and over again from the same articles you've written, instead of simply being paid a one-time fee. The Internet allows people to work from home and earn a lucrative income .

the best could be someone that paid you and continues to pay you, my affiliate programs are:
clickbank
primaryads
shareasale
revver
thenewsroom